Automatic follow-up focus detecting device and automatic follow-up device

ABSTRACT

An automatic follow-up focus detecting device comprises means for shiftably setting a follow-up field; extracting means for extracting a feature of an object in relation to the follow-up field; storing means for storing the extracted feature; detecting means for detecting a relative shift between the object and the device on the basis of the feature of the object extracted by the extracting means and the feature stored by the storing means; and shifting means for shifting a distance measuring field following the object according to the relative shift.

This is a continuation application of Ser. No. 07/701,691, filed May 14,1991; which in turn is a divisional application of Ser. No. 07/569,371,filed Aug. 14, 1990, now U.S. Pat. No. 5,031,049 which in turn is acontinuation of Ser. No. 07/483,998, Feb. 22, 1990; which in turn is acontinuation of Ser. No. 07/398,301, filed Aug. 24, 1989, now abandoned;which in turn is a continuation of Ser. No. 07/315,192, filed Feb. 23,1989; which in turn is a continuation of Ser. No. 07/183,482, filed Apr.15, 1988, now abandoned; and which in turn is a continuation of Ser. No.06/737,163, filed May 23, 1985, abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a device for automatically following a movingobject in carrying out focus detection and focus adjustment in a cameraand particularly in a video camera.

2. Description of the Prior Art

There have been proposed many automatic focus detecting devices of thekind arranged to use the video signal of a video camera as disclosed,for example, in the specifications of U.S. Pat. No. 2,831,057, JapanesePatent Publications No. SHO 39-5265 and No. SHO 46-17172, etc. Theseprior art devices employ different methods, which include one methodcalled "a mountain climbing control method". This method was disclosedin an article entitled "Automatic Focus Adjustment of TV Camera byMountain Climbing Servo Method", by Ishida, et al., appeared in "NHKTechnical Researches", Vol. 17, No. 1 (Serial No. 86), p. 21, published1965. Another method wherein mountain climbing control is employed incombination with a lens which is arranged to be focused by driving therear lens thereof was disclosed in a technical report entitled "ContourDetecting Automatic Focusing Method", by Hanma, et al. at a conferenceof a TV Society held Nov. 29, 1983.

Referring to FIG. 1A of the accompanying drawings, the prior art devicesof this kind have a distance measuring field fixedly positioned in themiddle of a picture taking plane. Therefore, when a main object to befocused on, which in this instance is a person, (hereinafter referred toas the main object) moves, the camera is focused on a wrong object (ahouse in this instance) instead of the main object as shown in FIG. 1B.Then, the image of the main object becomes a blur. FIGS. 1A, 1B, 2A and2B represent picture planes obtained with distance measurement performedby a camera which is provided with an automatic focusing device havingno parallax.

SUMMARY OF THE INVENTION

A first object of this invention is to provide an automatic follow-upfocus detecting device which is capable of obviating the above-statedshortcoming of the prior art devices by automatically detecting theposition of a moving object and by shifting a distance measuring fieldfollowing the movement of the object.

Under this object, an automatic follow-up focus detecting deviceembodying a first aspect of this invention comprises: Means forshiftably setting a follow-up field; extracting means for extracting afeature of an object in relation to the follow-up field; storing meansfor storing the extracted feature; detecting means for detecting arelative shift between the object and the device on the basis of thefeature of the object newly extracted by the extracting means and thefeature stored by the storing means; and shifting means for shifting adistance measuring field following the object according to the relativeshift.

A second object of this invention is to provide an automatic follow-updevice which is capable of stably performing an accurate follow-upoperation with a feature of an object registered by automaticallyadjusting a follow-up field to the position of the object.

Under this object, an automatic follow-up device embodying a secondaspect of this invention comprises: Registering means arranged to shifta follow-up field to a slight extent and to register a feature of theobject upon confirmation of that either the whole or a part of thefollow-up field come within the followup object; and follow-up meansarranged to perform a follow-up operation on the basis of the featureregistered by the registering means.

A third object of this invention is to provide an automatic follow-updevice which is capable of adjusting a follow-up field to the positionof an object without any error even in cases where a signal representinga feature of the object varies to a slight degree.

Under that object, an automatic follow-up device embodying a thirdaspect of this invention comprises: Means for detecting whether or notthe position of a follow-up field and that of an object to be followedup are in agreement with each other under a condition having a presetdead band; means for registering a feature of the object when theposition of the follow-up field and that of the object coincide witheach other; and means for folowing up the object on the basis of thefeature registered by the registering means.

A fourth object of this invention is to provide an automatic follow-updevice which is capable of stably shifting a set follow-up field inpursuit of the movement of an object to be followed up.

Under that object, an automatic follow-up device embodying a fourthaspect of this invention comprises: Means for shiftably setting afollow-up field; extracting means for extracting a feature of an object;storing means for storing the feature extracted; means for comparing afeature newly extracted by the extracting means with the feature storedby the storing means and for detecting whether there has arisen anychange exceeding a preset threshold value; and means for shifting thefollow-up field in the event of any change that exceeds the thresholdvalue.

A fifth object of this invention is to provide an automatic follow-updevice which is capable of satisfactorily following up an object,particularly, a person or persons within a scene.

Under that object, an automatic follow-up device embodying a fifthaspect of this invention comprises: Extracting means for extracting froma video signal obtained from within a follow-up field a feature of anobject as a color difference signal; storing means for storing the colordifference signal; detecting means for detecting a relative shiftbetween the object and the device on the basis of a color differencesignal newly extracted by the extracting means and the color differencesignal stored in the storing means.

A sixth object of this invention is to provide an automatic follow-updevice capable of accurately detecting with simple structuralarrangement the direction in which a relative shift between the deviceand an object takes place.

Under that object, an automatic follow-up device embodying a sixthaspect of this invention comprises: Setting means for setting afollow-up field which is divided into a plurality of regions; extractingmeans for extracting a signal representative of a feature of an objectbeing followed up from all of or some of the divided regions; anddetecting means for detecting a relative shift between the object andthe device on the basis of the extracted signal.

A seventh object of this invention is to provide an automatic follow-updevice which, in addition to attainment of the above-stated sixthobject, is capable of reducing the amount of computation to be performedby computing means in detecting a relative shift between the device andan object to be followed up.

Under that object, an automatic follow-up device embodying a seventhaspect of this invention comprises: Setting means for setting afollow-up field which is divided into at least three regions; extractingmeans for extracting at least two pairs of difference signals obtainedfrom signals representative of features of an object produced from thedivided regions which are adjacent to each other; detecting means fordetecting a relative shift between the object and the device on thebasis of at least two pairs of the extracted difference signals.

An eighth object of this invention is to provide an automatic follow-updevice which is capable of stably performing a follow-up operationwithout being affected by noises.

Under that object, an automatic follow-up device embodying an eighthaspect of this invention comprises: Extracting means for extracting asignal representing a feature of an object to be followed up;integrating means for integrating the signal extracted; detecting meansfor detecting a relative shift between the object and the device on thebasis of the signal integrated.

A ninth object of this invention is to provide an automatic follow-updevice which is provided with follow-up means capable of following up amoving object and particularly an object moving at a high speed.

Under that object, an automatic follow-up device embodying a ninthaspect of this invention comprises: Setting means for setting afollow-up field which is divided into at least three regions; extractingmeans for extracting at least two sets of difference signals out ofdifference signals obtained from signals which represent the features ofan object and are produced from at least two pairs of adjacent regionsincluding a middle region among the divided regions, with a signalobtained from the middle region fixed to be a signal representing afeature of the object at a specific point of time; and detecting meansfor detecting a relative shift between the object and the device on thebasis of the difference signals.

A tenth object of this invention is to provide an automatic follow-updevice which is capable of stably performing a follow-up operation indespite of variations in luminance of illuminating light.

Under that object, an automatic follow-up device embodying a tenthaspect of this invention comprises: Extracting means for extractingcolor difference and luminance signals representative of a feature of anobject to be followed up in relation to a follow-up field; and detectingmeans for detecting a shift of the object on the basis of a signalobtained by normalizing the color difference signal with the luminancesignal.

An eleventh object of this invention is to provide an automaticfollow-up device capable of accurately performing a follow-up operationwhich is prevented from becoming erroneous due to variations in ambientconditions.

Under that object, an automatic follow-up device embodying an eleventhaspect of this invention comprises: Storing means for storing a featureof an object to be followed up; determining means for determining ashift of the object; and renewing means for renewing the stored contentof the storing means according to the result of determination when theobject has been consecutively determined to be in a stationary state apredetermined number of times.

A twelfth object of the invention is to provide an automatic follow-updevice which is capable of always setting a follow-up field in a sizeapposite to an object despite of variations in distance to the objectand the focal length of a picture taking optical system.

Under that object, an automatic follow-up device embodying a twelfthaspect of the invention comprises: First detecting means for detecting adistance to an object; second detecting means for detecting the focallength of a photo-taking optical system; and setting means for settingthe size of a follow-up field according to the outputs of the first andsecond detecting means.

A thirteenth object of this invention is to provide an automaticfollow-up device which is capable of setting a follow-up field in anoptimum size for an object to be followed up.

Under that object, an automatic follow-up device embodying a thirteenthaspect of this invention comprises: Setting means arranged to permitmanual setting of a follow-up field in a variable size; registeringmeans for registering a feature of an object in relation to thefollow-up field; and detecting means for detecting a relative shiftbetween the object and the device on the basis of the feature of thefollow-up object registered.

A fourteenth object of this invention is to provide an automaticfollow-up device which permits the operator to set a follow-up field inan optimum size by carrying out fine adjustment while watching thefollow-up field as displayed on a display device.

Under the above-stated object, an automatic follow-up device embodying afourteenth aspect of the invention comprises: Setting means whichpermits manual setting of the size of a follow-up field in a variablemanner; display means for displaying the follow-up field on a displaydevice; registering means for registering a feature of an object inrelation to the follow-up field; and detecting means for detecting arelative shift between the object and the device on the basis of thefeature registered by the registering means.

These and further objects, aspects and features of this invention willbecome apparent from the following detailed description of preferredembodiments thereof taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Referred embodiments of this invention are described by way of examplebelow with reference to the accompanying drawings, in which:

FIGS. 1A and 1B show a relation between the image of an object and thedistance measuring field of the conventional camera, FIG. 1A showing aninstance where the distance measuring field is in agreement with theobject and FIG. 1B showing an instance where the object has moved.

FIGS. 2A and 2B show a relation between the image of the object and thedistance measuring field of a camera arranged according to thisinvention, FIG. 2A showing an instance where the object has moved toanother position at the same distance within an image plane and FIG. 2Bshowing another instance where the object has moved to a positionfurther away from the device within the image plane.

FIG. 3A shows a relation obtained between a followup field and theobject in case where the follow-up field is divided in a deviceembodying this invention. FIG. 3B shows the relation obtained with theobject having moved within the image plane of the device.

FIG. 4 is a block diagram showing a device arranged to process signalsobtained from the divided fields as shown in FIGS. 3A and 3B.

FIG. 5 is a graph showing the signals obtained from the device of FIG. 4as in a state of plotted on a two dimensional plane.

FIG. 6 is a block diagram showing a combination of an optical system andan electric control system arranged in a first embodiment of thisinvention.

FIG. 7 is a block diagram showing details of the essential parts of thedevice shown in FIG. 6.

FIG. 8 is an illustration of angular variations of signals obtained fromthe picture elements of a follow-up field in a second embodiment of thisinvention, the signals being shown as in a state of plotted on a twodimensional plane.

FIG. 9 is a graph showing signals obtained according to a thirdembodiment of this invention from the picture elements of the follow-upfield shown in FIGS. 3A and 3B, these signals being shown as in a stateof plotted on a plane of (R-Y/Y) and (B-Y/Y).

FIG. 10 is a block diagram showing by way of example an arrangement madein the third embodiment of this invention to obtain signals (R-Y/Y) and(B-Y/Y).

FIG. 11 is a block diagram showing an instance wherein the arrangementof FIG. 10 is applied to the device of FIG. 7.

FIG. 12 is a block diagram showing a device arranged to process signalsobtained from the picture elements of FIGS. 3A and 3B in carrying out anormalizing process by means of a distance computing circuit.

FIG. 13 is a block diagram showing an example of modification on thedevice of FIG. 11 for carrying out a normalization process by means of adistance computing circuit.

FIG. 14 is an illustration of a relation obtained between a follow-upfield and the image of an object with the object moving further to theright than in the case of FIG. 3B.

FIG. 15 is a graph showing by way of example signal obtained from thedivided follow-up field of FIG. 14 as in a stage of plotted on a twodimentional plane.

FIG. 16 shows another example of signals obtained from the dividedfields.

FIG. 17 is a block diagram showing the essential part of a fourthembodiment of this invention.

FIG. 18 is a block diagram showing a fifth embodiment of this inventionwhich is arranged to perform a reference color automatic renewingfunction.

FIG. 19 is a flow chart showing the reference color automatic renewingoperation of the device shown in FIG. 18 as the fifth embodiment of theinvention.

FIG. 20A is an illustration of a relation between an object and thefollow-up field of a sixth embodiment of this invention in which thefollow-up field is divided into picture elements extending both inhorizontal and vertical directions. FIG. 20B shows signals obtained fromthe picture elements of the embodiment shown in FIG. 20A as in a stateof plotted on a two dimensional plane.

FIG. 21 is a block diagram showing, like in FIG. 6, a combination of anoptical system and an electrical control system arranged as a seventhembodiment of this invention.

FIG. 22A shows a case where only one picture element is covering afollow-up object within a follow-up field. FIG. 22B shows another casewhere the object has moved to a different position within a pictureplane shown in FIG. 22A.

FIG. 23 shows signals obtained from the picture elements shown in FIGS.22A and 22B as in a state of plotted on a two dimensional plane.

FIG. 24A shows a case where all the picture elements within a follow-upfield are covering a follow-up object. FIG. 24B shows another case wherethe object has moved to a different position within a picture planeshown in FIG. 24A.

FIG. 25 shows signals obtained from the picture elements shown in FIGS.24A and 24B as in a state of plotted on a two dimensional plane.

FIG. 26 is a block diagram showing the details of a fine adjustment partarranged for the follow-up field of the device of FIG. 21, theillustration showing the details together with related parts.

FIG. 27A shows a relation between a follow-up field and an object in acondition where two of the picture elements within the follow-up fieldare not covering the background of a scene. FIG. 27B shows the samepicture plane as FIG. 27A as in a condition having the object shiftedits position therein.

FIG. 28 shows signals obtained from the picture elements shown in FIGS.27A and 27B as in a state of plotted on a two dimensional plane.

FIG. 29 is a block diagram showing the essential parts of an eighthembodiment of this invention.

FIGS. 30A and 30B show variations of signals (R-X) and (B-Y) relative totheir gate positions in the device shown in FIG. 29. FIG. 30C shows thepositions of an image of an object corresponding to the signalvariations shown in FIGS. 30A and 30B in relation to one of pictureelements within a follow-up field.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment I

The outline of the automatic follow-up or automatic follow-up focusdetecting operation of a first embodiment of this invention is asfollows: When a main object (a person) which is in a position within apicture plane as shown in FIG. 1A shifts its position to anotherposition in a right upper part of the same picture plane as shown inFIG. 2A without changing its distance from the distance of the originalposition, the shift of the object position is automatically detected byfollow-up means which will be described later. Then, the distancemeasuring field of the embodiment is shifted to follow the shift of theobject position to obtain a condition as shown in FIG. 2A. Theembodiment performs focus detection or focus adjustment with thedistance measuring field in the shifted position. More specifically, aparameter representing a feature of the object, such as the color of theobject itself and that of the background is extracted in relation to afollow-up field which is set by the above-stated follow-up means. Thefeature thus extracted is stored. Then, in case that the object moves orhas moved, the moving direction or moved position is detected on thebasis of the stored feature and a feature of the object newly extracted.With the moving direction or moved position detected, the follow-upfield is shifted following the shift of the object. Meanwhile, thedistance measuring field is also shifted in the same positional relationaccording as the follow-up field is shifted. Therefore, FIGS. 2A and 2Bmay be regarded as showing a relation between the shift of the objectand that of the follow-up field. The follow-up field is one of variedmeans for discerning a shift of an object. Normally, unlike the distancemeasuring field, the follow-up field is not displayed in the pictureplane of the view finder and the object is not observable through thefollow-up field. If the follow-up field is to be displayed on thepicture plane, one of the follow-up field and the distance measuringfield may be larger than the other on the picture plane as they arelocated in the same position on the picture plane. In the case of FIG.2A, since the object distance remains unchanged after the shift of theobject, the shift of position does not require any adjustment of thefocusing lens element within a picture taking lens. Whereas, in the caseof FIG. 2B, the object distance also changes while the object positionshifts to the right upper position within the picture plane. In thiscase, therefore, the focusing lens shifts its position according to theresult of distance measurement. Therefore, the size of the follow-upfield is changed by means of follow-up gate size determining means whichwill be described later herein. With the size of the follow-up fieldthus always adjusted to a size suitable for the object, the focusdetecting or adjusting operation is carried out under that condition.Since the shift of the object or the camera is relative to each other,the above-stated follow-up operation is effectively performed not onlyin cases where the object is moving while the camera is fixed but alsoin cases where the camera is moving while the object is in repose orwhere both the camera and the object are moving. Further, the size ofthe follow-up field is adjustable not only when the object distancechanges but also when the focal length of the lens changes.

In general, the follow-up field has a two dimensional spread. However,for the sake of simplification of description, the follow-up field is atfirst assumed to be one dimensionally extending, as shown in FIG. 3A,before describing it as having the normal two dimensional spreadextending in both the horizontal and vertical directions. Further, thefollow-up field is assumed to be divided into three parts or regions A,B and C (hereinafter these divided parts will be called pictureelements). Color difference signals (R-Y) and (B-Y) are obtained in theform of time series signals from each of these picture elements.Referring now to FIG. 4, these color difference signals are subjected tointegration, sample-and-hold and analog-to-digital conversion processeswhich are carried out by integrating circuits 100a and 100b,sample-and-hold (S/H) circuits 101a and 101b and analog-to-digital (A/D)conversion circuits 102a and 102b. The color difference signals thusprocessed are stored at memories 103a and 103b. By plotting these storedvalues on orthogonal axes (R-Y) and (B-Y) for the picture elements A, Band C, they can be expressed, for example, as shown in FIG. 5. Referringto FIG. 5, reference symbols A0, B0 and C0 respectively denote thesignals obtained from the picture elements A, B and C of FIG. 3A. Let usassume that, in this case, the picture element B produces a signalrepresenting only the dress of a person which is an object; the pictureelements A and C produce a signal obtained by adding up signalsrepresenting the dress and the background; and the color of thebackground of the left side of the object differs from that of thebackground on the right side of the object. Therefore, the points A0 andC0 are at different positions as color difference signal coordinates.

When the object shown in FIG. 3A moves to the right within the samepicture plane as shown in FIG. 3B, the ratio of a portion occupied bythe object to a portion occupied by the background within each of thepicture elements A and C comes to change. As a result, the signalobtained from the picture elements A and C change as shown at symbols A1and C1 in FIG. 5. Meanwhile, the picture element B remains within theimage of the object as shown in FIG. 3B. Therefore, if the dress or wearof the object is of a single color, the signal from the picture elementB does not change. Therefore, assuming that the points representing thesignals from the element B are B1=B0 for the sake of simplication, thepoint C1 is closer to the point B0 (=B1) and the point A1 is fartheraway from the point B0 (=B1) as shown in FIG. 5. A line segment B1-C1becomes shorter than a line segment B0-C0 while a line segment A1-B1 islonger than a line segment A0-B0. In case where the line segment B1-C1is longer than the line segment B0-C0 and the line segment A1-B1 isshorter A0-B0, this indicates that the object has moved to the left inthe picture plane of FIG. 3B. In case that the background is in the samecolor both on the left and right sides of the object, if the objectmoves to the right in the picture plane of FIG. 3B, the above-statedpoint A1 comes to a position on a line extending from the line segmentA0-B0 while the point C1 comes to a position on the line segment B0-C0.This invention is applicable to both of the cases mentioned above.

FIG. 6 shows the first embodiment of this invention which is based onthe concept described above. Referring to FIG. 6, a picture takingoptical system includes a focusing lens 1, a zoom system lens 2, adiaphragm 3 and a relay lens 4. An image of an object is arranged to bereceived by an image sensor 5 which is, for example a CCD. A clocksignal generating circuit 6 is arranged to have its output frequencydivided to a desired frequency by means of a frequency divider 7. Thefrequency divided output is arranged to be applied to an image sensordriving circuit 8, a follow-up gate setting circuit 11 and a distancemeasurement gate setting circuit 16. The image sensor driving circuit 8drives the image sensor 5 to cause it to produce a time series imagepick-up signal. The output of the image sensor 5 is subjected tonecessary synchronization signal composing, modulating and correctingprocesses through a signal processing circuit 9 and is thus formed intoa video signal, such as an NTSC signal. These processes are well knownto persons skilled in the art and thus the details of them are omittedfrom description here. In the following description, the video signalproduced from the signal processing circuit 9 is assumed to be an NTSCsignal.

At the same time as the NTSC signal, the signal processing circuit 9supplies color difference signals (R-Y) and (B-Y) to the follow-up gatesetting circuit 11 (which is provided for the follow-up field) and thedistance measuring gate setting circuit 16. The output of the follow-upgate setting circuit 11 is supplied to a color detecting circuit 12,which detects the color of the object. The detected color of the objectis stored at a memory 13, for example, via manual mechanical input meanssuch as a switch (not shown). The color detecting circuit 12 includesthe integrating circuit 100, the sample-and-hold circuit 101 and the A/Dconversion circuit 102 which are shown in FIG. 4. The above-statedprocessing operation is performed either in 1/60 sec. which is the onefield period of a television signal or according to an average value ofseveral field periods thereof. In the following description, theprocessing operation is assumed to be performed within one field periodor the averaged one field period.

During an ensuing field period, a signal newly extracted and the signalwhich is stored at the memory 13 are processed at a shift discerningcircuit 14. The circuit 14 thus detects whether the object has moved andthe moving direction thereof if it has moved. In the event that theobject has moved, a gate shifting circuit 15 controls the follow-up gatesetting circuit 11 to have the follow-up field shifted accordingly. Thesame operation (or computation) is then performed during the next fieldperiod. The above-stated processing operation is repeated untilcompletion of a follow-up process.

During the operation of the follow-up, the gate shifting circuit 15causes a distance measuring gate setting circuit 16 to set a distancemeasuring field in the same relative position as the follow-up field.Then, using a video signal obtained from the distance measuring field(the output of the signal processing circuit 9), an automatic focusing(AF) circuit 17 performs focus detection by a known method such as themountain climbing control method. A motor M is driven by the output ofthe automatic focusing circuit 17 to adjust the position of the focusinglens 1.

Again referring to FIG. 6, a position sensor P1 is arranged to detectthe absolute position of the focusing lens 1 corresponding to the objectdistance. Another position sensor P2 is arranged to detect the absoluteposition of the zoom system lens 2 corresponding to the focal length.Signals produced from these sensors are used by the follow-up gate sizedetermining circuit 10 in controlling the follow-up gate setting circuit11 and the distance measuring gate setting circuit 16 to have the sizesof the follow-up field and the distance measuring field thus determined.

Assuming that the focal length of the picture taking lens if f; theobject distance is R; the dimension of an image sensing surface in thelongitudinal direction is y; the length of the follow-up field (thetotal length of the picture elements A, B and C of FIG. 3A) is l; andthe length of the follow-up field covering the object is W and assumingl/y=k, there obtains the following relation: ##EQU1##

Assuming that, in a numerical example, f=30 mm; R=5000 mm; y=8.8 mm,and, assuming that the object being followed up is an adult person,W=500 mm, the value of k becomes: k=0.34.

The value of y is determined by the size of the image sensor, such as aCCD, and that of W by the object. Therefore, a size of the follow-upfield apposite to the object can be obtained from the output values ofthe position sensors P1 and P2 by computing the value k by the follow-upgate size determining circuit 10 in accordance with the formula givenabove.

The details of the above-stated color detecting circuit 12, the memory13 and the shift discerning circuit 14 are as shown in FIG. 7. Thesignals (R-Y) and (B-Y) of each of the picture elements A and B whichhave passed through the follow-up gate setting circuit 11 are applied toa distance computing circuit 21. The circuit 21 then gives the lengthDA0-B0 of the line segment A0-B0 on the coordinate system of signals(R-Y) and (B-Y) shown in FIG. 5. This value is stored at a memory 22.Then, a value DA1-B1 or DA1-B0 is likewise obtained from signals for anext field. Assuming that B1=B0 for the sake of simplification, thereobtains a relation DA1-B1=DA1-B0. Then, a divider 23 produces a valueDA1-B1/DA0-B0 through computation. This value is compared by acomparison circuit 25 with a first threshold value set by a thresholdvalue setting circuit 24. The comparison circuit 25 produces an output"1" in the event of a change to an extent exceeding the threshold value.Meanwhile, another sequence of circuits from a distance computingcircuit 31 to a comparison circuit 35 likewise computes and gives avalue DC1-B1/DC0-B0. The comparison circuit 35 likewise produces anoutput "1" in the event of a change exceeding a second threshold value.In a specific numerical example, with the first and second thresholdvalues both assumed to be 2 under the condition of FIG. 5, the followingvalues are obtained:

    DA1-B1/DC0-B0=2.2

    DC1-B1/DC0-B0=0.36

In this case, the comparison circuit 25 alone produces the output "1".Then, the shift discerning circuit 14 produces a signal for delaying agate setting timing for a predetermined length of time, which is, forexample about 1/125 of one horizontal scanning period in the case of theNTSC color system. Conversely, in case that the comparison circuit 35alone produces the output "1", the shift discerning circuit 14 producesa signal for quickening the gate setting timing by a predeterminedlength of time. In the latter case, the object has moved to the left asviewed on FIG. 3A.

The shift discerning circuit 14 thus produces a signal which changes thegate setting timing by a predetermined length of time according to theoutput "1" of the comparison circuit 25 or 35. In accordance with thissignal, the gate shifting circuit 15 controls the gate setting circuits11 and 16 as mentioned in the foregoing. The gate setting circuits 11and 16 then shift the follow-up field and the distance measuring fieldin the shifting direction of the object to permit focus detection to beperformed at the shifted position. When necessary, the stored valuesstored at the memories 22 and 32 may be renewed at the new position ofthe follow-up field obtained by following the shift of the object, sothat the signals can be repeatedly processed in the manner describedabove. In the specific example shown in FIG. 6, the follow-up gatesetting circuit 11 and the distance measuring gate setting circuit 16are arranged separately from each other. However, in practising thisinvention, the follow-up gate setting circuit may be omitted and theoutput of the distance measuring gate setting circuit 16 may be arrangedto be supplied to the color detecting circuit 12.

In the embodiment shown in FIGS. 6 and 7, as mentioned in the foregoing,the feature of a main picture taking object is extracted and stored; thefeature thus stored is compared with a newly extracted feature of themain object; a shift or no shift in the position of the main objectrelative to the device is judged from the result of comparison; and, inthe event of a shift in the relative position, the distance measuringfield is shifted following the shift of the object position. A focusdetecting or focus adjusting operation thus can be accomplished byautomatically following a moving object to be photographed. In additionto these functions, the embodiment is arranged to have the followingfunction or features:

1) The position sensors P1 and P2 and the follow-up gate sizedetermining circuit 10 are arranged to permit setting of a follow-upfield apposite to the object to be photographed even in the event of achange in the object distance or in the focal length of the photo-takinglens. Thus the follow-up can be accurately carried out.

2) The color of the object within the follow-up field is detected. Thisis then recognized as the position on a two dimensional coordinatesystem of color difference signals (R-Y) and (B-Y). The shift of theobject is detected from variations in the position. Therefore, thefollow-up can be satisfactorily accomplished by utilizing a differencein color between a dress or wear and the background in cases where theobject is a person. In the case of a video camera in particular, theautomatic follow-up device can be simply arranged, without necessitatingany change in the video signal processing system thereof, by utilizingthe color difference signals which are anyway necessary for video signalprocessing.

3) The follow-up field is divided into a plurality of regions or pictureelements, such as the picture elements A, B and C shown in FIG. 3A. Theshifting direction of the object can be detected in a simple manner byprocessing a video signal obtained from each of these divided regions orpicture elements. Further, the required amount of a computation processcan be reduced by utilizing a difference signal representing adifference between signals produced from adjoining picture elements. Inthe case of FIG. 3A, the follow-up field is divided into three pictureelements. However, the follow-up field can be divided into any increasednumber of picture elements. In that instance, depending on the manner inwhich the object moves, the shift in the position of the object isdetectable from color difference signals obtained from some of thepicture elements instead of all of the picture elements. Then, theminimum number of such difference signals that must be extracted is twopairs.

4) With the signal from each of the picture elements of the follow-upfield subjected to an integration process (circuits 100a and 100b ofFIG. 4), the operation of the embodiment can be stabilized without beingaffected by noises.

5) The threshold value setting circuits 24 and 34 are arranged to allowa follow-up action to be performed only in the event of occurrence of achange in excess of a predetermined value. This permits a stableoperation free from any hunting or overshoot. Furthermore, a dead bandin the follow-up action can be variable set through adjustment of thethreshold value.

6) The values stored at the memories 22 and 32 of FIG. 7 are arranged tobe renewable in a repeating manner as necessary according as theposition of the follow-up field shifts following the shift of that ofthe object, so that the processing operation described in the foregoingcan be repeatedly accomplished.

Embodiment II

In the preceding embodiment, color difference signal information is usedas a parameter indicative of a feature of the object to be photographed;and the signals (R-Y) and (B-Y) representing the features of the pictureelements are expressed as positions on rectangular coordinates. However,the coordinate system may be replaced with other coordinates such aspolar coordinates. Further, the signals representing the color of theobject may be either all of the three primary color signals R, G and Bor only some of them. Further, the feature of the object may beextracted by means of a parameter such as luminance signal informationor shape information. Such parameters may be used in combination withthe color signal information and the shape information combined witheach other.

In detecting a shift in the position of the object to be photographed bymeans of difference signals representing differences among signalsproduced from the picture elements A, B and C according as the objectmoves, a second embodiment of this invention is arranged to perform thisoperation as follows: Instead of detecting a change in the distancesbetween the positions of the color difference signals of pictureelements on the coordinates, i.e. instead of detecting the lengths ofline segments A0-B0, A1-B1, C0-B0, C1-B1, etc., the second embodimentperforms the shift detecting operation by detecting angular changes ofthese positions in a manner as shown in FIG. 8. When a person or anobject moves to the right within a picture plane, the ratio of an areaoccupied by the person to an area occupied by the background within eachof the picture elements A and C changes accordingly. As a result ofthis, the signals obtained from the picture elements A and C change asindicated by points A1 and C1 in the drawing. Meanwhile, the pictureelement B remains within the image of the person. Therefore, if thedress of the person can be regarded as a single color, the signalobtained from the picture element B remains almost completely unchanged.for the sake of simplification of description, points B1 and B0 areassumed to be the same as each other (B1=B0). Therefore, in thisinstance, the point C1 comes closer to the point B1 (=B0). Meanwhile,the point A1 moves away from the point B1 (=B0). In other words, anangle θA1-B1 across the origin O becomes larger than an angle θA0-B0. Anangle θC1-B1 becomes smaller than an angle θC0-B0. In case that theperson moves to the left within the picture plane, the angle θA1-B1becomes smaller than the angle θA0-B0 and the angle θC1-B1 larger thanthe angle θC0-B0.

In detecting a shift in the position of the object by utilizing theabove-stated phenomenon, angle computing circuits are arranged in placeof the distance computing circuits 21 and 31 which are shown in FIG. 7.The angles θA1-B1, θC1-B1, etc. on the coordinate system of the signals(R-Y) and (B-Y) are computed by these angle computing circuits and thefollowing values are obtained from the dividers 23 and 33:

θA1-B1/θA0-B0 and θC1-B1/θC0-B0

Then, in the same manner as in the case of the preceding example, thecomparison circuit 25 or 35 produces an output "1" and supplies it tothe shift discerning circuit 14 when either of these values comes toexceed a preset threshold value. In the case of FIG. 8, these valuesbecome:

    θA1-B1/θA0-B0=2.2 and θC1-B1/θC0-B0=0.36

In this instance, therefore, the comparison circuit 25 produces anoutput "1" to indicate that the object has moved to the right inrelation to the device. Then, the gate shifting circuit 15 of FIG. 6causes the follow-up field to shift in the shifting direction of theobject or person (or to the right as viewed on FIG. 8). Other functionsand operations of this embodiment are identical with those of thepreceding embodiment which is arranged to detect a change in distance.

In the embodiments shown in FIGS. 6, 7 and 8, a shift in the position ofthe photo-taking object being followed up is detected by detectingeither a change in distance between the positions representing thesignals of the picture elements on the coordinate system of signals(R-Y) and (B-Y), i.e. in the values

DA1-B1 and DC1-B1

or a change in the angular values

θA1-B1 and θC1-B1.

The arrangement of these embodiments, permits an adequate follow-upoperation on a person within a scenery by a difference in color betweenthe person's dress and the background. Further, in the embodimentdescribed, two color difference signals (R-Y) and (B-Y) are used fordetection. However, it is possible to detect the shift of object withonly one of the two color difference signals used instead of two ofthem. The shift detection also can be carried out by using some otherkind of information such as a characteristic contrast of the object incombination with such signals.

Embodiment III

In the case of the preceding embodiment, the shift of the object isdetected on the basis of the result of computation of the positions ofsignals of the picture elements A, B, C, etc. on the coordinate plane of(R-Y) and (B-Y). In that case, however, the positions on the system ofcoordinates would vary even when the object is not moving if theluminance of an illumination light varies with time. In other words, theposition comes closer to a zero point according as the illuminationlight becomes darker and comes farther away from the zero pointaccording as the light becomes brighter. This problem can be solved byextracting a luminance signal in addition to the color differencesignals (R-Y) and (B-Y); by dividing the two color difference signals bythe luminance signal to normalize them; and by computing theabove-stated values DA1-B1/DA0-B0 and DC1-B1/DC0-B0 on the coordinatesystem of the normalized signals R-Y/Y and B-Y/Y. This can beaccomplished as follows. For example, the luminance signals A(Y) andB(Y) of the picture elements A and B are supplied to the distancecomputing circuit 21 of FIG. 7 while the luminance signals B(Y) and C(Y)of the picture elements B and C are supplied to another distancecomputing circuit 31. Then, values R-Y/Y and B-Y/Y are computed by thesetwo computing circuits.

More specifically, the color difference signals (R-Y) and (B-Y) and theluminance signals Y are extracted from the picture elements mentioned inthe fore-going Then, these signals are processed through an arrangementwhich will be described later with reference to FIG. 10 to obtainnormalized signals by dividing the color difference signals (R-Y) and(B-Y) by the luminance signals Y respectively. The normalized signalsthus obtained is stored at memories which will be described later. Withthe stored signal values plotted on a rectangular coordinate system ofvalues (R-Y/Y) and (B-Y/Y) for each of the picture elements A, B and C,they can be expressed, for example, as shown in FIG. 9. In the case ofFIG. 9, the luminance of the illumination light is assumed to be in astandard condition.

A third embodiment of this invention is based on the above-statedconcept and is arranged as follows: As a result of a relative shiftbetween the positions of the object and the device, the signals obtainedfrom the picture elements A, B and C respectively shift on thecoordinate plane of values (R-Y/Y) and (B-Y/Y) from points A0, B0 and C0to points A1, B1 and C1. The relative shift of the object isautomatically detected by utilizing these changes. Then, the follow-upfield is automatically shifted following after the shift of the objectaccording to the result of detection. The reason for detecting the shiftof the position of the object by means of the signals obtained bynormalizing the color difference signals (R-Y) and (B-Y) is as follows:The purpose of automatic follow-up may be attained by detecting a shiftof the object position solely by means of color difference signals. Inthat case, however, the points on the color difference signal coordinatesystem might come to change, even when the object position remainsunchanged, if the luminance of the illuminating light varies with time.For example, each point on the coordinate system comes closer to a zeropoint when the illumination light becomes dark and comes farther awayfrom the zero point according as the light becomes brighter. Whereas, inthe case of the above-stated arrangement of this embodiment, theluminance signals Y are extracted from the picture elements in additionto the color difference signals (R-Y) and (B-Y) to obtain normalizedsignals (R-Y/Y) and (B-Y/Y) and the shift of the object position isdetected from the changes in the points representing the pictureelements and plotted on the rectangular coordinate system of values(R-Y/Y) and (B-Y.Y) as shown in FIG. 9. This arrangement permits stablefollow-up by automatically compensating for the variations in theluminance of the illumination light.

FIG. 10 shows by way of example a circuit arranged to obtain theabove-stated normalized signals (R-Y/Y) and (B-Y/Y). Referring to FIG.10, the color difference signals (R-Y) and (B-Y) are integratedrespectively by integrating circuits 100a and 100b. The integratedsignals thus obtained are sampled and held respectively bysample-and-hold (S/H) circuits 101a and 101b and are then supplied todividers 104a and 104b. Meanwhile, an incoming luminance signal Y isintegrated by another integrating circuit 100c. The integrated luminancesignal is then sampled and held at another sample-and-hold circuit 101cand is then supplied to the dividers 104a and 104b. These dividers 104aand 104b then produces the normalized signals (R-Y/Y) and (B-Y/Y)respectively. The normalized signals are A/D converted by A/D conversioncircuits 102a and 102b and are then stored at memories 103a and 103b.

In a modification of the above-stated circuit, the A/D conversioncircuits 102a and 102b are followed by dividers 104a and 104b; and thesampled and held signal Y is A/D converted before the normalizingprocess is carried out by the dividers 104a and 104b. In anothermodification, the dividers 104a and 104b are arranged before theintegrating circuits 100a and 100b; and the normalizing process may becarried out by supplying the signals (R-Y) and Y and signals (B-Y) and Yto the dividers 104a and 104b respectively.

The signals (R-Y/Y) and (B-Y/Y) which are obtained through thearrangement of FIG. 10 for each of the picture elements A, B and C aresupplied to the distance computing circuits 21 and 31 of FIG. 7 in placeof the signals (R-Y) and (B-Y) of the picture elements A, B and C asshown in FIG. 11. The follow-up operation is carried out on the basis ofinformation thus normalized by luminance.

In the embodiment described above, the normalizing process is carriedout by the circuit of FIG. 10. The outputs (R-Y/Y) and (B-Y/Y) thusobtained are processed by the distance computing circuits 21 and 31which are shown in FIG. 11. Meanwhile, in a modification of thisembodiment, the signals (R-Y), (B-Y) and Y are arranged to be obtainedthrough integrating, sample-and-holding and A/D converting processes asshown in FIG. 12 and are then supplied to distance computing circuits21' and 31' as shown in FIG. 13. Then, the normalizing process and thedistance computation on the rectangular coordinate system of values(R-Y/Y) and (B-Y/Y) are carried out through the circuit arrangementshown in FIG. 13. In FIGS. 12 and 13, the circuits which are arranged inthe same manner and to perform the same functions as those shown inFIGS. 4 and 7 are indicated by the same reference numerals as thoseshown in FIGS. 4 and 7. Further, the circuit arrangement shown in FIG.12 includes an A/D conversion circuit 102c and a memory 103c which areprovided for the signal Y.

In the embodiment described above, a shift in the position of the objectis detected by means of two color difference signals (R-Y/Y) and(B-Y/Y). However, in case that the change of color signals from each ofthe picture elements representing the features of the object and thebackground takes place mostly in one of the above-stated two signals,the shift of the object position can be detected solely by one of thesignals.

In cases where the luminance of an illumination light varies with time,the arrangement of the embodiment described above prevents each of thepoints on the coordinate system from coming closer to the origin O (whenthe light becomes darker) or from moving farther away from the origin O(when the light becomes brighter) while the object is not moving.

Embodiment IV

The device shown in FIGS. 2A-7 is arranged to operate on the basis ofthe result of a determining operation on the values DAn-Bn/DA0/B0 andDCn-Bn/DC0-B0 with the picture element B which is shown in FIG. 3Aassumed virtually to be B0=B1=B2= - - - =Bn. Whereas, a fourthembodiment of this invention is arranged to be capable of performingaccurate follow-up by detecting the position of a main object even incases where the object moves at a relatively high speed relative to thedevice.

In the event of a shift of the object at a relatively high speed, apoint representing the picture element B becomes B1=B0 within apredetermined period of time which is, for example, one fieldperiod=1/60 sec. Further, in case that the color of a new backgroundobtained by the shift is relatively close to the color of the object,there arises the following problem: Unlike the case of FIG. 3B, FIG. 14shows a case where the position of the object has shifted to a greatextent to the right within a period of 1/60 sec. FIG. 15 shows the shiftof points representing the picture elements on the rectangularcoordinate system of signals (R-Y) and (B-Y) after the shift of theobject. As shown, the point B1 shifts its position from a point B0toward a point A0. Assuming that a discerning threshold value is set at2 in the same manner as in the case of the shift discerning circuit ofFIG. 7, the values DA1-B1/DA0-B0 become about 1.5 in the case of FIG.15. In this instance, therefore, the shift discerning circuit 14 doesnot produce the output "1". Thus, it sometimes becomes impossible todetect a shift of the object even when the object moves fast.

FIG. 16 shows a more unfavorable case, wherein the positions of thepicture elements B and C on the coordinate system are close to eachother while those of the picture elements A and B are far away from eachother. In this event, the value DA1-B1/DA0-B0 sometimes does not reachthe threshold value 2 while, conversely, the value DC1-B1/DC0-B0 comesto exceed the threshold value 2. Under such a condition, the shiftingdirection of the object is sometimes judged to be moving in thedirection reverse to the actual direction.

The fourth embodiment is arranged to solve the above-stated problem. Themain feature of the embodiment resides in that a signal Bfix whichrepresents a feature of the picture element B of the middle region at aspecific point of time is employed as a follow-up reference instead ofthe signal obtained at the point Bn which varies every time the positionof the middle picture element B on the coordinate system changes.Although the signal B0 which represents a feature of the picture elementB obtained when an object is designated to be followed is preferablyused as the signal Bfix, the signal Bfix is not limited to the signalB0. Therefore, a shift of the object is discerned on the basis of thevalue DAn-B0/DA0-B0 instead of the value DAn-Bn/DA0-B0 and on the basisof the value DCn-B0/DC0-B0 instead of DCn-Bn/DC0-B0. In the case of FIG.15, the computed values of these values become DA1-B0/DA0-B0≈2.2 andDC1-B0/DC1-B0≈0.5. In the case of FIG. 16 they become DA1-B0/DA0-B0≈2.2and DC1-B0/DC0-B0≈0.5. The results of judgement are correct in bothcases.

FIG. 17 shows the essential parts of the fourth embodiment of thisinvention in a circuit diagram. This circuit corresponds to the circuitshown in FIG. 7. The optical system and the control circuit which areomitted from FIG. 17 can be arranged in the same manner as in theembodiment shown in FIG. 6. Referring to FIG. 17, a comparison circuitarrangement 50 is arranged to compare the above-stated valueDAn-B0/DA0-B0 with a threshold value KA. Another comparison circuitarrangement 51 is arranged to compare the above-stated valueDCn-B0/DC0-B0 which another threshold value KC. The values of the pointsA and B representing the color features of the picture element A and Bon the rectangular coordinate system of signals (R-Y) and (B-Y) arearranged to be applied to an input terminal 59. Upon receipt of aninstruction for initial setting, a switch 52 turns on. Then, a value A0for the picture element A and a value B0 for the picture element B arestored at a memory 53. Meanwhile, the points An and Bn are arranged tobe obtained at every interval of approximately n/60 sec. after scanningof scanning lines. In this instance in which n=0, the value of the pointAn on the rectangular coordinate system of signals (R-Y) and (B-Y) istransferred to a distance computing circuit 54. The term "distance" asused here means a distance between two points on the coordinate systemof signals (R-Y) and (B-Y). The computing circuit 54 thus receivesinformation on the points A0, B0 and An (A1 in the cases of FIGS. 15 and16). Then, the values DA0-B0 and DA1-B0 are respectively computedaccording to the following formulas: ##EQU2##

Then, the divider 55 computes these values obtained from the distancecomputing circuit 54 to produce a value DAn-B0/DA0-B0. The value thusobtained is compared at the comparison circuit 57 with the thresholdvalue KA which is set by a threshold setting circuit 56. In the event ofa change exceeding the threshold value KA, the shift discerning circuit58 produces the output "1" in the same manner as described in theforegoing. Another comparison circuit arrangement 51 also computes thevalue DCn-B0/DC0-B0 in the same manner as described above. Then, in theevent of a change exceeding another threshold value KC, the shiftdiscerning circuit 58 likewise produces the output "1". In the majorityof cases, the switch 52 is turned on virtually at the same timing inboth the comparators 50 and 51. Further, KA=KC.

With a shift of the object arranged to be judged on the basis of thevalues DAn-B0/DA0-B0 and DCn-B0/DC0-B0, the shift can be accuratelydiscerned and the automatic follow-up can be accurately carried out evenin cases where the object moves at a high speed relative to thefollow-up device.

Embodiment V

In the automatic follow-up focus detecting operation described above,there arises the following problem: If the signals A0, B0 and C0representing the color features of the picture elements, A, B and Cremain in the initially set state without being renewed, when a changeis brought about in color temperature by a change in the ambientconditions, the signal B which represents a color feature of the objecton the rectangular coordinates (R-Y) and (B-Y) comes to vary even whenthere is no change in the positional relation between the object and thepicture element B. In other words, the value DA1-B1 becomes larger thanthe value DA0-B0 and the value DB1-C1 larger than the value DB0-C0 whenthe ambient light becomes brighter to show a color difference moredistinctively. In that event, a shift in the position of the objectmight erroneously be detected depending on which of the two ratios firstcomes to exceed the above-stated threshold value.

A fifth embodiment of this invention is arranged to solve this problemand to be capable of permitting highly accurate automatic follow-upwithout any error even under such a changing ambient condition asmentioned above. FIG. 18 shows this embodiment. In FIG. 18, the samereference numerals as those used in FIG. 17 denote the same circuitelements and numerals with dash marks denote circuits elementscorresponding to those indicated by the numerals without dash marks inFIG. 17. In other words, a numeral 58' denotes a circuit correspondingto the shift discerning circuit 58 of FIG. 17. In this case, the circuit58' is arranged to produce a predetermined signal from its outputterminal 58'a when no shift of the object is detected in each cycle ofdiscerning operation. The embodiment includes a renewal control circuit105 which operates on the basis of the signal from the output terminal58'a of the shift discerning circuit 58' and is arranged to apply astandard color renewal instruction to the input terminal 59 of theswitch 52 in case that no shift of the object has consecutively beendetected a predetermined number of times (or cycles) or an "n" number oftimes. The renewal control circuit 105 is provided with a counter.

Referring to FIG. 19, the reference color automatic renewing operationof the device shown in FIG. 18 is as follows: When a follow-up action iscaused to begin by commencement of a photographing operation or under astand-by condition, reference setting is carried out for each of pointsA0, B0 and C0 at a step 60. This setting operation is performed with theswitch 52 turned on by the instruction from the control circuit 105 andwith the color features of the picture elements A, B, and C stored atthe memory 53. Steps 61 and 62 show the manner in which the shiftdiscerning circuit 58' forms a judgement or makes a discrimination. Ifthe result of the discrimination is "YES at the step 61 and NO at thestep 62" or is "NO at the step 61 and YES at the step 62", it indicatesthat the object has actually moved. In that event, the follow-up fieldis shifted in the applicable direction at a step 63 or 64. During theshift of the object, the set reference values of the points A0, B0 andC0 are not renewed. In case of the result of discrimination which is"YES at the step 61 and also YES at the step 62" or "NO at the step 61and also NO at the step 62", it indicates either that the object is inrepose or that the shift of the object is undiscernible. Thisdiscriminating action is preferably performed at every period of 1/60sec. In the latter case of discrimination, the number of times for whichthe latter discrimination is consecutively repeated is counted (at steps65 and 66). In that event, the above-stated count is cleared when adiscrimination of "YES and NO" or "NO and YES" is made once after the"NO and NO" or "YES and YES" discrimination has been consecutivelyrepeated an "m" number of times. At steps 67 and 68, it is determinedwhether the counted values of counters have exceeded a predeterminednumber "n" (n>m). In case that the discrimination "NO and NO" or "YESand YES" has been consecutively made more than the "n" number of times,a signal indicative of this fact is supplied from the control circuit105 to the switch 52 via the terminal 59. Upon receipt of this signal,the values of the points A0, B0 and C0 are renewed, that is, referencecolors are renewed at the step 60. Assuming that the shift discerningcircuit 58' is arranged to make a discriminating action at intervals of1/60 sec., and that the "n" number is 5, the reference colors arerenewed when the object remains still for a period of 1/12 sec.

Accordingly, with the reference color renewing means added in thismanner, the storage contents of the storing means which is arranged tostore the feature of the object (the memory 53 in the case of FIG. 18)can be renewed. This arrangement effectively prevents erroneousdiscernment of a shift of the object due to a change in the ambientconditions, so that follow-up can be carried out at a high degree ofprecision.

Embodiment VI

The foregoing embodiments of this invention are arranged to detect onedimensional shift of the object position, i.e. a shift in the horizontaldirection. In order to adequately cover a two dimensional shift of theobject, it is preferable to have a follow-up field arranged to extendboth in horizontal and vertical directions as shown in FIG. 20A.Referring to FIG. 20A, picture elements A, B and C are arranged toextend in the horizontal direction in the same manner as in the case ofFIG. 3A. In the case of a sixth embodiment, however, the follow-up fieldfurther includes picture elements A' and C' which are arranged tovertically extend from the middle picture element B. Forsimplification's sake, let us assume that a person which is a mainphoto-taking object is wearing a single color dress while the color ofthe background portion covered by the region or picture element Adiffers from that of another background portion covered by the pictureelement C. FIG. 20B shows the color features of these picture elementsA, B, C, A' and C' as expressed on rectangular coordinate axes (R-Y) and(B-Y). The color features of the picture elements A' and C' differ fromeach other to a slight degree under the influence of light and shadowsas the dress of the object is of a single color. However, compared withthe picture elements A and C which are under the influence of thebackground, the picture elements A' and C' are plotted closer to a pointB. In cases where the object or the camera is moving only in thehorizontal direction, changes take place substantially in the samemanner as in the case of FIG. 3B. However, in the event of a movement ofthe object or the camera in the vertical or oblique direction, thepositions of the picture elements A' and C' on the plane of axes (R-Y)and (B-Y) vary to a great degree as the background comes to enter thesepicture elements A' and C'.

With the follow-up field arranged to extend both in the vertical andhorizontal directions as shown in FIGS. 20A and 20B, the relative shiftbetween the object and the camera is detected in the following manner:In addition to a first shift detecting system arranged as shown in FIG.6, there are provided another shift detecting system. The former is usedfor detecting a shift in the horizontal direction and the latter fordetecting a shift in the vertical direction. The outputs of a total offour comparison circuits for these two shift detecting systems arearranged to be supplied to a common shift discerning circuit, such asthe circuit 14 of FIG. 7. When, for example, the shift discerningcircuit receives information from the first shift detecting system abouta shift in the leftward direction and information from another about anupward shift, the circuit determines that the object has moved in theleft upward direction within a picture plane relative to the camera.

Embodiment VII

A seventh embodiment of this invention is arranged to permit fineadjustment of the follow-up field described in the foregoing. Referringto FIG. 21, the embodiment includes a follow-up field fine adjustmentcircuit 40. As will be further described with reference to FIG. 26 laterherein, the circuit 40 is arranged to effect fine adjustment of the sizeof the follow-up field by controlling a follow-up gate setting circuit11 in accordance with an input I from a manual operation member 38. Thecircuit 40 forms a signal indicative of the size of the finely adjustedfollow-up field and combines it with an incoming NTSC signal. Acomposite signal thus obtained is arranged to be displayed at a displaydevice 39 of an electronic view finder (EVF) or the like. The rest ofthe arrangement of this embodiment is similar to the arrangement of theembodiment shown in FIG. 6. Further, the shift discerning or determiningpart of this embodiment is arranged in the same manner as in the case ofFIG. 7.

In the case of FIG. 3A, the relation between the follow-up field and theobject is arranged on the assumption that a boundary line between theleft background and and the object is approximately in the middle partof the picture element A and a boundary line between the rightbackground and the object approximately in the middle part of thepicture element C when the device is in its registering mode. Deviationfrom this condition might make shift discernment impossible in anensuing comparison mode. The reason for this is as described below withreference to FIGS. 22A, 22B to FIG. 26:

FIG. 22A shows a case where the object which is being followed up isregistered in a state of being covered solely by the picture element B.In this instance, assuming that the outputs of picture elements A, B,and C are A0, B0 and C0, these outputs are expressed, for example, on acoordinate system (R-Y) and (B-Y) as shown in FIG. 23. Next, assumingthat the object being followed up shifts its position to the left withinthe picture plane as shown in FIG. 22B, the positions of outputs A1, B1and C1 then become, for example, as shown in FIG. 23. Under thiscondition, values DA1-B1/A0-B0 and DC1-B1/C0-B0 becomes as shown below:

DA1-D1/A0-B0=0.6,

DC1-B1/C0-B0=0.5

Therefore, in this instance, both the comparison circuits 25 and 35 ofFIG. 7 produce an output "0" and it becomes impossible to detect theshift of the object by the arrangement of FIG. 7 alone. FIG. 24A showsanother instance where the object to be followed up is covered by allthe picture elements A, B and C and is registered in that state.Assuming that the outputs of these picture elements are A0, B0 and C0,they are expressed, for example, on a coordinate system (R-Y) and (B-Y)as shown in FIG. 25. When the object moves to the left relative to thepicture elements within the same picture plane as shown in FIG. 24B, thepositions of outputs A1, B1 and C1 of the picture elements become asshown in FIG. 25. Under this condition, the values DA1-B1/A0-B0 andDC1-B1/C0-B0 become as shown below:

DA1-B1/A0-B0=0/0=indefinite

DC1-B1/C0-B0=n/0=∞ (wherein "n" represents a number.)

Then, the comparison circuit 35 produces an output "1". However, sincethe output of another comparison circuit 25 is indefinite, the shiftdiscerning circuit sometimes correctly determines the object to havemoved to the left relative to the device but sometimes incorrectlydetermines it to have moved in the reverse direction. Further, since thedenominators of both the values DA1-B1/A0-B0 and DC1-B1/C0-B0 are closeto zero, the outputs of the comparison circuits 25 and 35 becomeunstable and thus tend to result in an unstable follow-up operation.

To solve these problems, the seventh embodiment is provided with afollow-up field fine adjustment circuit 40 and is arranged to permitmanual setting of the size of the follow-up field at the time of aregistering process. FIG. 26 shows the details of the seventhembodiment.

Referring to FIG. 26, the follow-up field fine adjustment circuit 40includes a combiner 41; a follow-up field display circuit 42; and inputdevice 43; and a follow-up gate size fine adjustment circuit 44 whichare interconnected as shown in the drawing. Other parts which areindicated by the same reference numerals as those used in FIGS. 6 and 26are arranged and function in the same manner as the corresponding partsshown in FIGS. 6 and 26.

In a follow-up object registering mode, a follow-up field is set in astandard size (a little larger than the body of the object in this case)by the follow-up gate setting circuit 11. A display signal of a sizecorresponding to the set size of the follow-up field is formed by thefollow-up field display circuit 42. This display signal is combined withan NTSC signal by the combiner 41 into a composite signal. Thiscomposite signal is displayed at the display device 39 of an electronicview finder or the like. The photographer then confirms that thefollow-up field is of a size suited for the object to be followed up(see FIG. 3A). If it is too small or too large for the object as shownin FIG. 22A or FIG. 24A, the manual operation member 38 is operated tohave a signal for increasing or decreasing the size of the follow-upfield supplied from the input device 43 to the follow-up gate size fineadjustment circuit 44. Upon receipt of this signal, the follow-up gatesize fine adjustment circuit 44 supplies the follow-up gate settingcircuit 11 with a signal for causing fine adjustment of the follow-upfield to be effected. Then, in response to this signal, the follow-upgate setting circuit 11 sets the size of the follow-up field. Then, theadjusted follow-up field is again displayed at the display device viathe follow-up field display circuit 42 and the combiner 41. Thephotographer observes it and repeats the fine adjustment until the sizeof the follow-up field becomes apposite to the object to be followed up.Upon completion of the fine adjustment, the object is registered and thedevice enters into a follow-up mode.

The arrangement of this embodiment thus permits the follow-up field tobe set in a size best suited to each of varied sizes of objects to befollowed up.

Embodiment VIII

The arrangement of the embodiment described above might result in amisjudgement of a shift of the object during the process of thecomparison mode ensuing the registering mode, depending on the conditionunder which the position of the follow-up field is adjusted to thefollow-up object during the process of the registering mode. Forexample, let us assume that the feature of the follow-up object isregistered under a condition having no signal of the background enteringthe picture elements B and C as shown in FIG. 27A. Under this condition,signals from the picture elements can be plotted on a rectangularcoordinate system (R-Y) and (B-Y) as indicated by points A0, B0 and C0in FIG. 28. After that, if the object shifts to the right relative tothe picture elements or the device as shown in FIG. 27B, the signalsfrom the picture elements can be plotted as indicated by points A1, B1and C1 in FIG. 28. In this instance, the values DA1-B1/DA0-B0 andDC1-B1/DC0-B0 become as shown below:

DA1-B1/DA0-B0=0.67,

DC1-B1/DC0-B0=∞

Therefore, in the circuit arrangement shown in FIG. 7, the comparisoncircuit 35 produces an output "1"; and the shift discerning circuit 14produces a signal for quickening the gate setting timing by apredetermined length of time. As a result of that, the follow-up fieldis shifted in the direction reverse to the object to be followed up.

To solve this problem, an eighth embodiment of this invention isarranged as follows: Before the feature of the object is registered, thefollow-up field is shifted to a slight extent until either the whole ofor a part of the follow-up field is stably set within the image of theobject. FIG. 29 shows the circuit arrangement of this embodiment. Inthis embodiment, the feature of the object is registered afterconfirmation of the stabilization of the middle picture element B withinthe image of the object to be followed up. With respect to what part ofthe follow-up field is to be used for the confirmation of theabove-stated condition, it may be determined according as required bydesign work.

Compared with the device shown in FIG. 6, the device shown in FIG. 29differs in the additional provision of a positioning circuit 71. In FIG.29, the parts which are arranged to perform basically the same functionsas the corresponding parts of FIG. 6 are indicated by the same referencenumerals. Meanwhile, the overall arrangement of this embodiment isbasically the same as that of the embodiment shown in FIG. 6 and,therefore, is omitted from the illustration in FIG. 29. As shown, thepositioning circuit 71 includes a color difference signal momory 72, aninitial gate shifting circuit 73, a gate position memory 74 and aninitial setting circuit 75.

Referring now to FIGS. 30A, 30B and 30C, the operation of thisembodiment in its registering mode is as follows: FIGS. 30A and 30B showthe variations of signals (R-Y) and (B-Y) relative to gate positionswhich arise when the relative positions between the object and theabove-stated picture element B are as shown in FIG. 30C. Assuming that agate position is "0" when the relative position between the pictureelement B and the object is as shown in FIG. 27A. Under this condition,a registering mode is initiated by a manual setting operation on aswitch or the like which is not shown. First, information on the gateposition "0" shown in FIG. 30A is stored at the gate position memory 74.Then, color difference signals (R-Y) and (B-Y) of values shown in FIG.30A are stored at the color difference signal memory 72. The initialgate shifting circuit 73 then shifts the position of the picture elementB to the left as viwed on FIG. 27A to a predetermined extent, forexample, as much as 1/3 of the length of the picture element.Information on a gate position "-1" which is thus obtained then is oncestored at the gate position memory 74. At the same time, the colordifference signals (R-Y) and (B-Y) are stored at the color differencesignal memory 72. The initial setting circuit 75 then compares the colordifference signals obtained at the time of the gate position "-1" withthe color difference signals obtained at the time of the gate position"0". In this instance, both the signals (R-Y) and (B-Y) have changed toan extent exceeding predetermined threshold values (or dead bands) ERand EB. The picture element B is regarded as having deviated from theobject and processed when any one of the color difference signals (R-Y)and (B-Y) has changed to an extent exceeding the applicable thresholdvalue. In the event of changes in the two color difference signals to anextent exceeding these threshold values with the gate position shiftedfrom "0" to " -1", the stored value within the gate position memory 74for the gate positions "-1" and "0" and the stored value within thecolor difference signal memory 72 for the gate position "-1" are clearedrespectively.

Next, the initial gate shifting circuit 73 shifts the position of thepicture element B for the gate position "0" in the reverse direction,i.e. to the right as viewed on FIG. 27A to a predetermined extent whichis, for example, 1/3 of the length of the picture element to obtain agate position "1". With the gate position thus changed to "1", the sameprocess and comparison are carried out as in the above-stated instance.In this instance, both the color difference signals (R-Y) and (B-Y) donot change to any extent that exceeds the threshold values. With boththe signals not changing to any extent exceeding the threshold values,the picture element B is regarded as staying within the image of theobject. In this case, a value obtained by subtracting 1 from the storedvalue of the gate position memory 74, i.e. "0", is stored at the gateposition memory 74. Meanwhile, the stored value of the color differencesignal memory 72 for the gate position "1" is cleared. Then, the sameoperation as described above is also performed for another gatepositions. When it comes to the gate position "4", if the colordifference signal (R-Y) alone changes to an extent exceeding thethreshold value, the picture element B is considered to have deviatedfrom the image of the object. In that instance, a value obtained bysubtracting 1 from the stored value of the gate position memory 74, thatis, "3" is stored at the memory 74. Meanwhile, the stored value of thecolor difference signal memory for the gate position "4" is cleared.

As a result of the above-stated processes, the values "0" and "3" arestored at the gate memory 74. Then, on the basis of these stored values,intermediate values between these stored values, such as "1" and "5" aregiven to the initial setting circuit 73. At the same time, the storedvalue of the color difference signal memory 72, i.e. the signals (R-Y)and (B-Y) for the gate position "0", is applied to the memory 13. Withthe picture element B thus having been stably set within the image ofthe object, a registering operation comes to an end (an input to thememory 13, in this specific example). Thus, in the embodiment described,the gate or the follow-up field is shifted to a slight extent andconfirmation of a condition in which either the whole or a part of thefollow-up field has settled within the image of the object is madebefore a feature of the object is registered as a reference value foruse in the operation in the ensuing comparison mode. Therefore, thisarrangement ensures stable and accurate follow-up. Further, thediscrimination as to whether the picture element of the follow-up fieldhas deviated from the image of the object is arranged to be accomplishedthrough comparison with the threshold value, that is, with a dead bandprovided for the discrimination. Therefore, this arrangement precludesthe possibility of erroneous positioning even in cases where the colordifference signals which represent the features of the object vary onlyto a slight degree.

While preferred embodiments have been described in the foregoing, thisinvention is of course not limited to these examples. Many and variouschanges and modifications may be made in the invention without departingfrom the spirit and scope thereof. Further, this invention is applicablenot only to video cameras but also to a wide range of other apparatusesthat are arranged to perform a follow-up action on a moving object.

What is claimed is:
 1. An automatic follow-up focus detecting devicecomprising:means for shiftably setting a follow-up field; extractingmeans for extracting a feature of an object in relation to the follow-upfield; storing means for storing said extracted feature; detecting meansfor detecting a relative shift between said object and the device on thebasis of the feature of said object newly extracted by said extractingmeans and the feature stored by said storing means; and shifting meansfor shifting a distance measuring field following said object accordingto said relative shift between said object and the device.
 2. A videocamera, comprising:(A) a photographing optical system for photographingan object and for focusing an image of the object on an image sensingplane; (B) image sensing means for converting the image of the object onsaid image sensing plane into an image sensing signal; (C) area settingmeans for setting a detecting area for extracting a feature of saidimage of the object on said image sensing plane; (D) detecting means fordetecting the feature of said image from said image sensing signalcorresponding to said detecting area, and for putting out correspondingsignals; (E) first control means for detecting a variation of said imageof the object on the basis of an output of said detecting means and forcontrolling said area setting means so that said detecting area followsthe variation of said image of the object; and (F) second control meansfor varying a size of said detecting area in response to a focal lengthof said photographing optical system.
 3. A video camera according toclaim 2, wherein said detecting means detects a color signal componentin said image sensing signal.
 4. A video camera according to claim 2,wherein said detecting means includes normalizing means for effectingnormalization on the basis of a luminance, in order to prevent thesignal representing the feature of the image extracted from said imagesensing signal from being subjected to an influence of a brightness. 5.A video camera according to claim 1, wherein said first control means isarranged to detect a shift of said image by comparing the output of saiddetecting means at different timings.
 6. A video camera according toclaim 5, and further comprising integrating means for integrating theoutputs of said detecting means, wherein said first control means isarranged to detect the shift of the image by comparing the signalssmoothed by said integrating means.
 7. A video camera according to claim2, wherein said detecting area is a focus detecting area.
 8. A videocamera, comprising:(A) a photographing optical system for photographingan object and for focusing an image of the object on an image sensingplane; (B) image sensing means for converting the image of the object onsaid image sensing plane into an image sensing signal; (C) area settingmeans for setting a detecting area for extracting a feature of saidimage of the object on said image sensing plane; (D) detecting means fordetecting the feature of said image from said image sensing signalcorresponding to said detecting area, and for producing outputs; (E)first control means for detecting a variation of said image of theobject on the basis of an output of said detecting means and forcontrolling said area setting means so that said detecting area followsthe variation of said image of the object; and (F) second control meansfor varying a size of said detecting area in response to a distancebetween said object and the video camera body.
 9. A video cameraaccording to claim 8, wherein said detecting means includes normalizingmeans for effecting normalizing on the basis of a luminance, in order toprevent the signal representing the feature of the image extracted fromsaid image sensing signal from being subjected to an influence of abrightness.
 10. A video camera according to claim 8, wherein said firstcontrol means is arranged to detect a shift of said image by comparingthe outputs of said detecting means at different timings.
 11. A videocamera, comprising:(A) image sensing means for converting the image ofthe object on said image sensing plane into an image sensing signal; (B)area setting means for setting a detecting area for extracting a featureof said image of the object on said image sensing plane; (C) detectingmeans for detecting the feature of said image from said image sensingsignal corresponding to said detecting area, and for producing anoutput; (D) control means for detecting a variation of said image of theobject on the basis of an output of said detecting means and forcontrolling said area setting means so that said detecting area followsthe variation of said image of the object; and (E) adjusting means formanually varying a size of said detecting area.
 12. A video cameraaccording to claim 11, wherein said control means includes a memory forstoring the output of said detecting means and it is arranged to detecta shift of said image by comparing the output of said detecting means atdifferent timings.
 13. A video camera according to claim 11, whereinsaid detecting means includes normalizing means for effectingnormalization on the basis of a luminance in order to prevent the signalrepresenting the feature of the image extracted from said image sensingsignal from being subjected to an influence of a brightness.
 14. A videocamera, comprising:(A) area setting means for setting a detecting areafor detecting a feature of an image in a picture plane; (B) detectingmeans for detecting the feature of said image in said detecting areafrom the image signal; (C) control means for detecting a variation ofsaid image on the basis of an output of said detecting means and forcontrolling said area setting means so that said detecting area followsthe variation of said image when the variation of said image comesbeyond a predetermined threshold value; and (D) means for varying saidthreshold value.
 15. A video camera according to claim 14, wherein saidthreshold value determines a non-sensitive band for the shift of saiddetecting area.
 16. A video camera according to claim 14, wherein saiddetecting area is a focus detecting area.